1. Field of the Invention
The invention relates to a rotation angle detection device and a rotation angle detection method that are applied to vehicles such as passenger automobiles, trucks, buses, etc.
2. Description of the Related Art
As a rotation angle detection device that detects the rotation angle of a steering wheel of a motor vehicle, that is, the steering angle, an absolute angle sensor type device as described in Japanese Patent Application Publication No. 2007-127609 (JP-A-2007-127609) has been disclosed. This type of rotation angle detection device includes a main gear that is pivoted integrally with a column main shaft coupled to a steering wheel, two detection gears that are meshed with the main gear, and that each have a built-in magnet and that have different numbers of teeth, two magnetic resistance elements that face the magnets and that each magnetically detect the rotation angle of a corresponding one of the two detection gears, and a microcomputer that computes and detects the rotation angle of the steering wheel from the output waveforms of the magnetic resistance elements.
In this rotation angle detection device, the numbers of teeth of the two detection gears are different from each other, so that the periods of the detection waveforms of the two magnetic resistance elements are deviated from each other. On the basis of the detected waveforms, detection angle is computed. Therefore, it is possible to detect the detection angle that univocally corresponds to the rotation angle, in a relatively broad unit range of angle rotation.
However, the foregoing rotation angle detection device described in Japanese Patent Application Publication No. 2007-127609 (JP-A-2007-127609) has a problem as follows. That is, in the case where the range of the rotation angle that is a detection object of the column main shaft deviates from the unit range of the rotation angle detection device, that is, in the case where a mounting error occurs, the detection angle that univocally corresponds to the rotation angle cannot be detected without going through the mounting operation again, and therefore a cost increase will result.